Field of the Invention
The invention relates to a building material, using bast fibers and a binder, and to a method and an apparatus for producing such a building material.
Building materials based on synthetic and mineral raw materials or synthetic and mineral semifinished materials are known. It is also known that these materials may include natural fiber materials. Such materials are for example used for the interior trim of automobile doors. Moldings are produced based both, on duroplastics and on thermoplastics as a matrix. These moldings are reinforced by glass fibers, bast fibers, sisal and the like. The matrix may be foamed in order to reduce the weight. Fibers from bast fiber plants, which are completely or substantially free of shives, are used for this purpose. A higher shive fraction is acceptable in the case of flax and oil linen than in the case of hemp and jute, since they are finer.
Wood fragments from bast fiber plants, which are formed when the bast fibers are separated from the ligneous core, are called shives. For this purpose, the stalks are fed in full length or in portions of the stalk to corresponding apparatuses. The apparatuses break up the brittle wood core into fragments and at the same time separate the bast fiber from the wood. By "scutching" or "tangle fiber hackling" and subsequently using machines for cutting off residual shives from the fibers, either an almost shive-free long fiber or a tow with a certain residual shive fraction is then produced.
Depending on the structure of the production plant, short fibers with a relatively high shive fraction and relatively low-fiber shives are produced as a byproduct. The short fibers, of a length of between two and thirty millimeters, are freed of the residual shives in further process steps and are sold mainly to the paper industry, in particular the cigarette paper industry. The substantially fiber-free shives have to be disposed of. According to most recent developments, decortication, i.e. removing the wooden materials, is already carried out in the field, so that the shives, for which there is hardly any use at the present time, can be left directly as waste in the field. In earlier decades, the fibers from bast fiber plants were used predominantly for the production of clothing textiles and industrial textiles (ship's sails, ropes, tarpaulins, tents and the like). These textiles have since been largely replaced by synthetic fibers. With growing ecological awareness, attempts are being made, throughout the world, to reintroduce bast fibers. The main field of use is nonwovens for the production of interior fittings and equipment of passenger vehicles and for insulating purposes in the building industry.
After being decorticated, the fibers have to undergo a number of costly cleaning and opening operations. These operations inevitably shorten the fibers and they become pliable and soft. However, nonwovens made from soft fibers will collapse. Since they become too dense when they collapse, they are difficult to impregnate with thermoplastic melts or are difficult to impregnate evenly. This also applies to the spray-coating or cast-coating of thermosets or duroplastics of a synthetic or a biological type. Due to the collapsing, these materials lose some of their insulating value, when used as fleeces for insulating materials. Synthetic fibers, which prevent collapse due to their brittleness, therefore have to be admixed. Shives are, in principle, extremely light wood, almost as light as balsa wood. They are rigid and brittle and possess a fibrous structure. Their density is in the range of between 250 and 350 kg/M.sup.3. After breaking, they do not have a very high degree of fineness. In contrast to shives, fibers from bast fiber plants, also short fibers, have a very high strength and a very high degree of fineness. Customarily, bast fibers and shives are always thoroughly separated, since, for further processing operations with the currently available machines and technologies for the production of fleeces, mats and balls, as well as for spinning and for currently known products, shives have a disruptive effect and oftentimes even make processing impossible.